1. Field of the Invention
The present invention relates to a projection lens shifting mechanism, and more particularly a projection lens shifting mechanism that enables two-dimensional adjustment of a projection lens.
2. Description of the Related Art
Conventionally, the projection lens of a projector is fixed, and the position of the picture projected onto the screen is therefore determined by the relative position or angle of the screen and projector. In order to project a picture of proper position onto the screen, the projector must be adjusted to the proper relative position with respect to the screen, and considerable time and effort are therefore required to position the projector.
When the projector is set up, and it is desired to shift the position of the picture on the screen still higher, the projection direction is shifted upward by means of a height adjustment mechanism attached to the forward legs of the projector. In such a case, however, since the angle between the projection lens and the screen surface changes, the picture that should be projected, for example, as a square is distorted to a trapezoid.
To solve this problem, a type of projection lens shifting mechanism as shown in FIG. 1 has been developed. The position of the picture on the screen can be shifted by said projection lens shifting mechanism 1 when the projector is set up.
The projection lens shifting mechanism I comprises: a driving wheel 11, a worm 12, two fixed bars 13,14, four pedestals 151,152,153,154 and a movable plate 16. The four pedestals 151,152,153,154 are secured on a base plate 17, and form a plane parallel to the surface of the light valve of the projector (not shown in the figure). The first fixed bar 13 is secured to the pedestals 151,152, whereas the second fixed bar 14 is secured to the pedestals 153,154. Worm 12 is attached to one end of driving wheel 11, and they have the same central axis and are joined to the first fixed bar 13; therefore, they can rotate with respect to the first fixed bar 13.
Movable plate 16, on which a projection lens 18 is mounted, has a gear rack 161 and a U-shaped jaw 162 on one side, and two sleeves 163,164 on the other side, wherein the gear rack 161 engages with the worm 1, the U-shaped jaw 162 slidably clamps the first fixed bar 13, and two sleeves 163,164 are slidably joined to the second fixed bar 14.
When driving wheel 11 rotates due to an external torque, worm 12 rotates accordingly. Then, worm 12 drives the gear rack 161 so as to make movable plate 16 translate in the vertical direction. U-shaped jaw 162 and two sleeves 163,164 can restrict the direction of translation of movable plate 16.
When the projection lens shifting mechanism 1 is operated manually, the user applies force against the driving wheel 11 in the horizontal direction, but the movable plate 16 translates in the vertical direction. Such interface is not user friendly. In addition, said shifting mechanism only provides one-dimensional movement, which cannot achieve two-dimensional movement. Furthermore, the engagement of worm 12 and gear rack 161 cannot provide high resolution positioning.
Consequently, there is a need for a novel and improved projection lens shifting mechanism to solve above-mentioned problem.